Add sizing-4.vim

https://www.w3.org/TR/2020/WD-css-sizing-4-20200526/

after/syntax/css/sizing-4.vim

@@ -0,0 +1,2 @@
+syn match cssFontProp contained "\<contain-intrinsic-size\>"
+syn match cssFontAttr contained "\<\fit-content\>"

test/test.css

@@ -852,6 +852,11 @@ mask {
 	display: fit-content(10%);
 }
 
+.sizing-4 {
+	contain-intrinsic-size: auto;
+	display: fit-content;
+}
+
 .speech-1 {
 	voice-volume: auto;
 	voice-balance: auto;